physical - Physical Layer Rudra Dutta ECE/CSC 570 - Fall...

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Physical Layer Physical Layer Rudra Dutta ECE/CSC 570 - Fall 2007, Section 001
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Copyright Fall 2007, Rudra Dutta, NCSU 2 Context Context Lowest of OSI layers Provides a bit pipe More communications than networking We want to understand: General techniques Theoretical results
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Copyright Fall 2007, Rudra Dutta, NCSU 3 Communication Links Communication Links Various technologies for physical communication Copper wire, coax, fiber, radio, satellites, … Single underlying phenomenon - EM waves One way to utilize the phenomenon - guide Copper, glass Another way – no guide Free space (“wireless cable”) Radio, optical (Smoke signal? Semaphore? Magnetic tapes? Pigeons (supersonic or otherwise) ?)
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Copyright Fall 2007, Rudra Dutta, NCSU 4 EM Waves EM Waves Energy can carry information More correctly, distribution of energy EM waves carry energy, hence information Amplitude, frequency, phase Modifications (“modulations”) of these carry information
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Copyright Fall 2007, Rudra Dutta, NCSU 5 Digital or Analog ? Digital or Analog ? Digital – concept Information can be analog or digital EM waves – analog by definition Analog EM signal can be made to transfer digital data Thus we could (and usually do) have: “Digital interpretation of analog signal representing digital representation of analog data” 010100…
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Copyright Fall 2007, Rudra Dutta, NCSU 6 Propagation Media Propagation Media Guided Twisted pair Coax cable Optical fiber Unguided Radio (semi-guided follow curvature of earth) Radio bounced off ionosphere Fiberless optical (wireless optical) Communication satellites
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Copyright Fall 2007, Rudra Dutta, NCSU 7 Communication in the EM Spectrum Communication in the EM Spectrum
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Copyright Fall 2007, Rudra Dutta, NCSU 8 Modulation Modulation A “carrier” wave exists on the medium Own amplitude, frequency, phase Base energy pattern – no information Analog, of course A “signal” needs to be transmitted Time varying; analog, or digital The value of the signal from instant to instant is used to change the energy pattern of the carrier
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Copyright Fall 2007, Rudra Dutta, NCSU 9 Injection Injection Baseband No carrier, modulation
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physical - Physical Layer Rudra Dutta ECE/CSC 570 - Fall...

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